Unskilled contractors make up most of the workforce and face higher doses of radiation than utility employees at Fukushima and other nuclear power plants in Japan.

Reporting from Namie, Japan — Kazuo Okawa's luckless career as a "nuclear gypsy" began one night at a poker game.

The year was 1992, and jobs were scarce in this farming town in the shadow of the Fukushima Daiichi nuclear power plant. An unemployed Okawa gambled and drank a lot.

He was dealing cards when a stranger made him an offer: manage a crew of unskilled workers at the nearby plant. "Just gather a team of young guys and show up at the front gate; I'll tell you what to do," instructed the man, who Okawa later learned was a recruiter for a local job subcontracting firm.

Okawa didn't know the first thing about nuclear power, but he figured, what could go wrong?

He became what's known in Japan as a "jumper" or "nuclear gypsy" for the way he moved among various nuclear plants. But the nickname that Okawa disliked most was burakumin, a derisive label for those who worked the thankless jobs he and others performed.

Such unskilled contractors exist at the bottom rung of the nation's employment ladder, subjecting themselves to perilous doses of radioactivity.

Solicited from day labor sites across the country, many contractors are told little of the task ahead.

"The recruiters call out their windows that they have two days of work; it's not unlike the way migrant farm workers are hired in the U.S.," said Kim Kearfott, a nuclear engineer and radiation health expert at the University of Michigan.

"Many are given their training en route to the plant. They're told: 'Oh, by the way, we're going to Fukushima. If you don't like it, you can get off the truck right now.' There's no such thing as informed consent, like you would have in a human medical experiment," she said.

After an earthquake-triggered tsunami deluged the Fukushima plant in March, a disaster that cascaded into reactor core meltdowns, activists are calling for better government regulation of what they call the nuclear industry's dirtiest secret.

For decades, they say, atomic plants have maintained a two-tiered workforce: one made up of highly paid and well-trained utility employees, and another of contractors with less training and fewer health benefits.

Last year, 88% of the 83,000 workers at the nation's 18 commercial nuclear power plants were contract workers, according to Japan's Nuclear and Industrial Safety Agency, a government regulator.

A study by the Citizens' Nuclear Information Center, a Tokyo-based watchdog group, found that contractors last year accounted for 96% of the harmful radiation absorbed by workers at the nation's nuclear power plants. Temporary workers at the Fukushima plant in 2010 also faced radiation levels 16 times higher than did employees of the plant's owner-operator, Tokyo Electric Power Co., because contractors are called in for the most dangerous work, according to the government's industrial safety agency.

"This job is a death sentence, performed by workers who aren't being given information about the dangers they face," said Hiroaki Koide, an assistant professor at Kyoto University's Research Reactor Institute and author of the book "The Lie of Nuclear Power."

Okawa, who was off work from the plant the day of the tsunami, immediately quit the job and the "suicidal work" he performed there: mopping up leaks of radioactive water, wiping down "hot" equipment and filling drums with contaminated nuclear waste.

He described an unofficial pecking order at most nuclear plants among contractors, with the greenest workers often assigned the most dangerous jobs until they got enough experience to question the work or a newer worker came along.

"In the beginning, you get a little training; they show you how to use your tools," said Okawa, 56. "But then you're left to work with radiation you can't see, smell or taste. If you think about it, you imagine it might be killing you. But you don't want to think about it."

Okawa, a small man with powerfully built hands, said contractors knew they faced layoff once they reached exposure limits, so many switched off dosimeters and other radiation measuring devices.

"Guys needed the work, so they cut corners," he said. "The plant bosses knew it but looked the other way."

Now the Fukushima plant needs its temporary workers more than ever, to help Tokyo Electric Power Co. engineers shut down the stricken reactors for good. The "gypsies" are being paid salaries several times higher than before the accident, says Okawa, who says he was offered $650 a day to return to work at Fukushima after the reactor meltdowns there.

On a recent day, hundreds of contractors milled about an abandoned soccer complex near the Fukushima plant that Tokyo Electric Power Co., known as Tepco, has transformed into a nuclear-worker locker room and debriefing center. Men waited in line to pick up dosimeters and disposed of dirty clothes from a just-completed shift. Buses packed with blank-faced workers ran continuously between the center, known as J-Village, and the plant a few miles away.